Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an improved method for making manually
disruptable container closures.
More specifically the present invention pertains to providing an improvement
in l:he method disclosed in the cited Canadian Patent 1,016,~16 whereby an
integral but fractured section may be more reliably and predictably created
in even the alloys of tougher metals, for instance in sheet steel as well as in
sheet aluminum.
J' The referenced method of providing a weakening line in a sheet metal
lid, which line is characterized by being a fractured but integral section,
10 contemplates that after a sheet metal closure has, at least in part, been
defined by depressing the lid to provide the bounding wall of its closure,
a lengthwise indentation by shear-coining will then be made in that formed
wall to effect the fractured section. It has since been discovered that when
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practicing that method on tougher metal alloys, for instance sheet steel
instead of aluminum, it can often be difficult to precisely and sufficiently
control the tougher sheet material to attain the exact degree of fracture
desired or required by means of the subsequent coining operation.
Presumably this is largely due to the fact that the metal of the closure wall
in the locality to be fractured is, when the prior practice is pursued, under
compression and therefore resisting penetration by the coining tool. In
softer sheet material this may not be disadvantageous, but in work
on sheet steel material, for instance, from which easy-open can tops
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or the like are to be made, in addition to the more obvious blunting effect
upon the coining die, a less consistently uniform degree of fracturing may
:, result with consequently unsatifactory, because less predictable, strength
~` being imparted to the juncture of the lid with its closure.
In view of the foregoing, it is an object of this invention to provide an
improved method of making sheet metal container closures to be defined at
least in part by a fractured but integral section.
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Another and more general object of this invention is to provide a more
reliable and eEfective method for consistently producing precision weakening
lines in sheet metal, such as steel, whereby subsequent manual rupture thereof,
even after swaging of the metal adjoining the lines, can be achieved with
substantially uniform predetermined pressure.
To these encls, and as here;n shown, our novel process involves bending
the sheet metal of a container lid portion to peripherally form and at least partly
define a closure having a wall with a ridge extending on one side of the lid, -
and concurrently coining the closure wall to indent one side of the wall in a
longitudinal locality under tension due to the bending thus creating a rupturable .,,!
fractured but integral section between the closure and the lid. In performing
the metal forming and coining concurrently rather than in steps sequence,
cer~ain advantages of importance are gained. As the coining tool impinges
against a locality of one side of the closure wall, the sheet metal of that wall
is being bent and consequently subjected to tensional stress imparted by forming
dies. As the bending curvature increases and coin indenting becomes deeper,
unit tension becomes greater at the critical locality where a controlled fracture
of the wall is desired. Under these conditions the critical degree of fracture
can now be precisely and repeatedly produced. Toughness in the sheet metal
is now not an adverse factor either as to augmenting compression of the metal
in resisting coining to the required degree of penetration or as to creating
the degree of fracture desired.
Additionally the invention enables benefits in the form of simpler organiza-
tion of the tooling employed in practicing the novel method. The concurrent
forming and coining to render the closure weakening line fractured but integral
with its cover or lid facilitates a double swaging to be attained for properly sealing
the locality OI fracture as disclosed in our Canadian Patent 1,016,416.
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According to the above objects and features of the
present invention, there is provided a method of making
digitally disruptable line in sheet metal having opposite
generally planar surfaces,which method consists in substan-
tially simultaneously bending a portion of the metal to form
a wall with a locality bowed in tension adjacent to one surface
thereof, and longitudinally coinlng the tensioned surface and
locality of the wall as it is being thus bent,to create in
the residuum thickness adjacent to the opposite surface of
the wall locality, a fractured but integral section defining
the said line.
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The foregoing and other features of the invention will
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now be more particularly described in connection with an illus-
trative embodiment and with references to the accompanying
drawings thereof, in which:
Figure 1 i9 a perspective view of one product afforded
by use of the invention, a can top produced by the present
m~thoc1 and havlng a closure adapted to be manually openable,
Fiyure 2 is a vertical section of cooperative closure
forming and coining dies taken when looking in the direction of
the arrows II-II in Figure 1 and prior to operation of the dies,
Figure 3 is a section similar to Figure 2 but at a
moment later in the course of relative movement of approach of
the dies concurrently to bend and coin, and
Figure 4 is a section similar to Figure 3 and showing
the bottoming of the concurrent bending and coining to create a
fractured but integral weakening line, which thereafter may be
~" urged as by s1~aging into "closed" or sealed condition. `
While it will be appreciated that this invention is ;-
broadly useful in creating a tear line in sheet metal, the inven-
` 20 tion has particular utility in the formation of so-called "easy ;
open" metal containers 10, for instance in their can ends 12, an
illustrative one of which is shown in Figure 1. Neither the
, shape of -the can end 12 or of the general configuration of a ;
manually disruptable closure 14 to be formed therein by the
present method need be limitecl to circular, such shapes being
herein shown merely for convenience.
`` As taught in Canadian Patent No. 1,016,416 issued
0` August 30, 1977, the closure 14 i9 characterized by having at
least a portion of its periphery defined by a specially fractured
~ 30 but integral section 16 (Figures 1, 4) sometimes more generally
`~ ; referred to as a tear or weakening line. The degree of fracture,
especially when fluid pressures are -to be reliably retained in
the container L0, is clearly crit~cal. Moreover,
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it is highly important to be able to uniformly and repeatedly create the fractured
but integral section 16, even in tougher sheet metal, so that intentional opening
of the completed closure can be gained manually with the exertion of only a
normal, fairly predictable pressure. The novel technique for accomplishing
such fractured weakening lines will next be explained with reference to sequential
Figures 2-4.
A planar or nearly planar metal sheet 18 (Figure 2) from which the container
portion 12 is formed or to be formed is first suitably positioned and supported
in substantially unrestrained manner between a lower forming die 20 coaxial
with a coining tool 22, and an upper forming die 24. These dies are relatively
movable together and apart along a vertical axis. In more usual practice and
as here assumed, the coining tool 22 is stationary, but not necessarily so,
and the upper die 24 is reciprocable. The coining tool 22 may be integral,
but is herein shown non-integral, with a sleeve 26 slidably holding the lower
forming die 20 which may ultimately serve as a knock out for ejecting the can
end with its completed closure 14. Optionally when so desired, the sleeve 26
being independently and relatively movable heightwise with respect to the tool
22, swaging surface 40 of the sleeve can act on the sheet 18 prior to effecting its
ej ection .
The upper forming die 24 is formed with an annularly projecting rounded
portion 28 which, as illustrated in Figure 3, is arranged during a working
stroke to engage the sheet 18 and bend it by imposing a trough therein in a recess
defined by the upper end of the forming die 20, the sleeve 26, and the upper
end of the coining tool 22. The tool 22 is formed with an internal vertically
disposed annular cutting edge 30, an adjoining angularly related coining face
32, and an outer inclined face 34. The faces 32 and 34 are disposed to engage
the convexly flexed under surface of the sheet 18, preferably outwardly of
a ridge 36 being imposed by the portion 28. Thus the technique employed
and being described is such that the sheet metal is being bent and formed thus
to concomitantly subject it to stretching tension (as indicated by arrows A and B
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in E'igure 3) in a longitudinal locality and this same locality ~-
is concurrently being coined by the face 32,
As the relative movement of approach of the foLming
die 24 bottoms as shown in Figure ~, penc~?tration of the ten-
~ ione~ mater:ial 18 bv the edges 30 and khe face 32 has proceededprecisely to the re~uired depth to produce the desired weaken-
ing line at the fractured but integral section 15. This syn-
chronous coining and bending to produce tension in the locality
being coined ~acilitates attainment of a precise, and when
desired, a uniforrn degree of fracture, even in tougher metals
such as steel, which is difficult to produce by the procedures
hitherto known, It appears that by coin indenting sheet metal
which is undergoing'tensional stress rather than compression
(except compression due to action of the coining tool), the metal
does not "fight" the coining penetration to the same extent even ' '
though the rnetal is considered of a tougher character such as ;
steel. ~ot only is service life of the coining tool increased as a
consequence of improved metal flow, but more importantly as
previously noted, the fractured but integral section 16 extend-
ing at the bottom of the penetration can reliably be given the
exact residuum dimension re~uired in the closure 14 or for any
particular wea~ening line. In a typical sheet steel can end,
for instance, the residuurn or fractured section may be roughly
about 1/3 the sheet thickness. '
It will be ~Inderstood that following the concurrent
bending to form with tension and the coining to fracture,
thereby at least partially deEining the closure 14, subsequent "
closure making steps as hitherto taught for instance, as in
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U. S. patents 3,881,437 and 3,881,630 both issued on May 6,
1975, may follow. ~hus, a single or double swaging (not shown)
' may next be applied, single swaging by top surface 40 of the
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sleeve 26, for instance, to flow and enlarge wall metal
adjacent to the fractured section 16 thereby tending to close
and lock it to the can end 12. A coating of lacquer may lastly
he applied to the weakening line 16 and/or the whole end 12.
Combining the initial step of closure forming while fracturing,
as one op~xation, enables the subsequent steps to produce
closures 14 assuring reliable and consistently uniform operat-
ing character.
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